Dynamic Magnetic Susceptibility of Quantum Spin Liquid

Abstract

In this chapter, we consider the dynamic magnetic susceptibility of quantum spin liquid, based on the theory of fermion condensation. The obtained results show that the dynamic magnetic susceptibility behaves as that of HF metals. Therefore, two known classical types of magnetism (ferro- and antiferromagnetism) can be augmented by one more, caused not by the order of the magnetic moments of atoms, ions, or electrons, but by the “liquid” behavior of spins. A new magnetic state of matter emerges, which is characterized by a spins flow. This flow is described by means of virtual chargeless particles—spinons, behaving as HF liquid. The theory of the dynamic magnetic susceptibility allows us to reveal that at low-temperature quasiparticles excitations, or spinons, form a continuum, and populate an approximately flat band crossing the Fermi level. The obtained results are in good agreement with experimental facts collected on herbertsmithite \(\mathrm{ZnCu_3(OH)_6Cl_2}\) and as well as on HF metals, and allow us to predict a new scaling in magnetic fields in the dynamic susceptibility. Under the application of strong magnetic fields, quantum spin liquid becomes completely polarized. We show that this polarization can be viewed as a manifestation of gapped excitations when investigating the spin-lattice relaxation rate.